To wire spotlights
to work together with your high beams is not that difficult.
diagram below shows a simple wiring diagram for connecting spotlights
to work together with your high beams.
All you need is some wire and lugs, a 12V 4 Pole relay and two fuse
holders with the correct fuses. Just make sure that you use decent
sized wires and a proper fuse holder for the connection of the power
between the battery and the relay as well as the spot lights. If the
wires and the fuse holder are too small then you might have the problems
with under performance of the spots because of the high resistance
of thinner wires and smaller connectors, it inhibits the delivery
of enough current to the spotlight. For optimal performance use 2.5
mm or thicker wire and a decent bakelite type (or something similar)
fuse holder that can handle the current flow Do not use the white
plastic ones, like the ones at the back of your car radio, as they
tend to overheat with the high current that can be drawn by the spotlights
A good idea is to solder the wires to the wire lugs. What I do in
such a case is to use lugs without the plastic sleeves (or remove
the plastic) and then isolate the lug afterwards with heat shrink
sleeve, which you can buy from most decent electrical or auto spares
The correct fuse size can be determined easily. The formula for power
is: P=V x I with “V “being the voltage and “I”
the current. Current flow (amps) is thus the power, i.e. the combined
watts rating of the spots, divided by 12V. Thus 2 x 55Watt spots will
use 110/12=9.2A. Thus, you can use a 15 Amp fuse for the main circuit.
Firstly, connect the earth wire of the spotlights to the chassis of
the vehicle at any existing screw using round lugs. Make sure the
surface underneath the nut or bolt is not painted and the metal is
bare to ensure proper connectivity. A possible idea is to earth the
wires onto the negative pole of the battery. Also connect pin 85 of
the relay to an earth, possibly using the same screw that secures
Now connect a wire between the batteries’ positive (+ / red)
pole and pin 30 of the relay with the bakelite fuse holder in this
wire, but do not insert the fuse yet. Pin 87 is connected to the positive
wires of the spotlights.
Pin 86 will be connected to the existing wire that feeds your high
If you need to determine which wire on the existing light to connect
pin 86 of the relay to, it is very easy to determine. Use a test light/meter.
There are 3 wires that feed the existing globe.
One of the wires is the negative or ground wire. The other two are
the positive wires, one for the low beam and one for the high beam.
The latter is the one you need. Ground your test lamp/meter somewhere
on the body or the battery’s negative terminal and switch the
high beam on. If your test lamp or leads does not have a sharp point,
use a needle and stick it into the first wire. If the test lamp goes
on then you have the correct wire. If not try the other wires as well.
By only ‘pricking’ the wires, you will not really damage
Once you have determined the wire you can skin the wire only for a
few millimetres and solder the new wire on and insulate the joint
properly afterwards. If your vehicle is still under warrantee or you
do not like to skin the existing wires you can use one of the clip
on connectors that many of the tow-bar fitment guys use to connect
the tow-bar’s wiring to the existing vehicle wiring. This is
a small plastic connector with a metal clip inside and if you clamp
it onto a wire the contacts inside cuts though the insulation and
makes contact with the wires inside.
Since that wire only powers the relay which draws very little current
a 1 amp fuse should be enough. The reason for such a small fuse
it that if this wire short circuits it will blow and not affect
the use of your headlights or blow their existing fuses.
If you want the extra control of switching your spot lights off
when the high beams are switched on for instance when the spotlights
are covered an extra switch can be connected in the relay’s
earth wire connected to pin 85
want to wire more than one set of spotlights
it is advisable to use an extra relay for every set of spotlights.
Lets say you want to wire one set of spots with 2x 100w globes and
another with 2x55w globes the total current will be 26A. Most of
the relays' that you buy over the counter have a maximum rating
of 30 amps, so running a circuit at almost the relay's maximum capacity
is not a good idea. In general one never use an electric/electronic
component at higher then 60-70% of its maximum rating. Furthermore
the lugs might overheat and for 26 amp you would need fairly thick
wires as well, so I would suggest rather to wire each set of spots
on their own circuit with their own relay.
You can connect the wires of pin 86 and 85 (the control circuit)
back to to the first relay so that all relays switch on simultaneously.
Or if you want to take it one step further and make the different
sets of spotlights to switch separately you can place individual
switches on each relays pin 85 and the connect all switches back
to a common earth.
by Eric Skeen